Interesting tactic here, they must feel confident it won't be too bad, basically challenging the league to not appeal
I mean, the appeal goes to one Roger Goodell for the final decision, so the NFLPA knows an appeal won't get them anywhere if the punishment is harsh, and it could result in harsher punishment if the punishment is light and the NFL uses the appeal process.
To borrow an analogy I head on sports radio on my way home tonight, the NFLPA has a slingshot and is asking the NFL to mutually put down their arms while the NFL has an uzi. There's no chance the appeals process lightens any penalty given out. There's plenty of chance that it lengthens it. So of course they're going to ask the NFL to not use it.
I suspect if the suspension is 8 games, the NFL may accept that even though they might like more so that they don't get the bad PR of overruling the mutually agreed upon judge, but any less than that and I suspect the NFL steps in and goes bigger via the appeal process that is heavily slanted in their favor.